Make sure your ready to boot from install media by changing the boot order
Remember to press any key when prompted at the start of the new install. If you miss the prompt windows won't install.
Install Windows 10, when it asks for a key simply click 'I don't have one'. As long as you did the proper upgrade from 7 to 10 then it will be added automatically once your online and signed in with your Microsoft account.
Do not reattach your new drive yet. Let's see if we can get win 10 running smoothly first.